SPERMATOGENESIS CHAP 10

Certain requirements of spermatogenesis

• Adequate secretion of GnRH

• FSH & LH secretion

• secretion of gonadal steroids (testosterone and estradiol)

NO _____ center in the male

Surge center

• 4-8 episodes/24 hours

• FSH has >3x half-life of LH

• Inhibin secretion by Sertoli cells → inhibits FSH

Spermatogenesis happens in the

seminiferous tubule

under control of FSH

LH acts on _______ cells

Leydig cells

• leydig cells = theca interna cells

• Receptors for LH

• LH binds to receptors

• Synthesize P4 - which is then converted to testosterone (T)

For spermatogenesis to be constant, ___ must also be constant

Testosterone → LH → GnRH

• LH must be pulsatile for normal testicular function (prevents leydig cells from becoming refractory)

T concentrations in testes are much _______ than T conc. in blood

HIGHER (100-500X)

• high T required for spermatogenesis

Testes also secrete ________

estradiol

• especially in boars and stallions

• relevance - probably neg. feedback on hypothalamus with T

Sertoli cells are ____ dependant

FSH

• sertoli cells = granulosa cells

• convert T to E2 and dihydrotestosterone (DHT)

• secrete inhibin - supress FSH

Spermatogenesis

• Takes place entirely within seminiferous tubules

• 3 phases:

  • Proliferation phase → all mitotic divisions of spermatogonia

  • Meiotic phase → haploid spermatids (1N)

  • Differentiation phase → transformation into spermatozoa

Proliferation Phase

All mitotic divisions of spermatogonia

• continuous stem cell renewal - allows new spermatogonia to develop

• each generation has cytoplasmic bridges - synchronized cohort

• some degenerate throughout process

• results in primary spermatocytes

• Specialized diploid (2N)

• A1-A4, I (intermediate) and B spermatogonia

• Pool of stem cells - continual source of A-spermatogonia

Meiotic phase

Begins w primary spermatocytes

Meiosis I:

• Gentic diversity - DNA replication and crossing over during production of secondary spermatocytes

• No 2 sperm are identical

Meiosis II:

• results in haploid spermatids (1N)

_________________ protects spermatocytes from immune cells

Blood-testis barrier

Meiotic phase continued

Reduces the number of chromosomes to haploid

• DNA synthesis and replication

• Crossing over - random assortment of different segments of each chromosome

• genetic diversity

Differentiation Phase

• No further cell division

• from spherical undifferentiated spermatid to fully differentiated, specialized spermatozoa

• nucleus becomes highly condensed

• acrosome is formed

• cells become potentially motile

Differentiation phase PHASES

• Golgi phase

• Cap phase

• Acrosomal phase

• Maturation phase

Golgi phase (A, B, & C)

= acrosomic vesicle formation

• packages acrosomal contents and membranes

Acrosome

contains enzymes

a cap-like, membrane-bound organelle located at the tip of the sperm head, derived from the Golgi apparatus during spermatid development

Golgi phase A

• Newly formed spermatid is spherical

• Well developed golgi apparatus

  • many small vesicles

  • golgi will give arise to acrosome

Golgi phase B

• proacrosomic granules form and fuse

• centroles migrate to base of nucleus

Golgi phase C

• Acrosomic vesicle contains dense acrosomic granule

• smaller golgi vesicles are continually added

• Proximal centriole - implantation apparatus that allows flagellum to anchor to nucleus

• Distal centirole - gives rise to axoneme (flagellum)

Cap phase

= acrosomic vesicle spreads over nucleus

• Distal centriole - gives rise to axoneme (flagellum)

• Acrosomal vesicle flatens and forms distinct cap

  • outer acrosomal membrane

  • inner acrosomal membrane

  • enzymes

Acrosomal phase

• spermatic elongates

• acrosome coves most of antirior nucelus

• manchette forms - some microtubules will be postnuclear cap

• neck and annulus form

• plasma membrane surounds all

Maturation phase

• Mitochondria migrate and form a spiral = middle piece

• postnuclear cap - formed from manchette

• annulus - juncture between middle and principle piece

• plasma membrane!!

As maturation occurs, cell move from the __________ toward the _________

As maturation occurs, cell move from the basement membrane toward the lumen

Spermitation

release of spermatozoa from Sertoli cells into lumen

• analogous to ovulation, except occurs continuously throughout testis

Spermatozoa =

Head + Tail

Head =

nucleus + acrosome + post-nuclear cap

• In mammals, head shape differs between specis

• Nucleus is oval & flattened → nuclear membrane

Chromatin

the material of which the chromosomes of organisms other than bacteria (i.e., eukaryotes) are composed. It consists of protein, RNA, and DNA.

In spermatozoa, chromatin is _________

keratinized

• disulfide bonds

• transcription and translation stop

• protects DNA after spermiation until fertilization

• reversed after fertilization

The process of nuclear condensation (keratinization & DNA stability) is reversed only ________ the sperm enters the oocyte cytoplasm

The process of nuclear condensation (keratinization & DNA stability) is reversed only AFTER the sperm enters the oocyte cytoplasm

Antiorior (front) 2/3 of nucleus is covered by _________

Acrosome

→ is a lysosome

• Hydrolytic enzymes: Acrosin, Hyluronidase, Zona lysin, Esterases, Acid hydrolases

Acrosome reaction

• during fertilization

• Ordered, highly specialized exocytosis

• allows release of enzymes

• digests zona pellucida

How do we prevent more than one spermatozoa to fertilize oocyte?

Chemical reactions that harden outer layers in oocyte

**in class talking, not on exam**

Tail =

middle piece + principle piece + terminal piece

self propelled flagellum

Middle piece - where energy is utilized

Differentiation between males and females:

Male has to have constant and continuous spermatogenesis!

• always ready

____ week delay before negative effects on spermatogenesis are observed in ejaculated sperm

2-4 weeks

• heat stress

• shipping

• fever

• exposure to certain toxins

6-12 weeks until complete restoration of spermatogenesis afterwards

Spermatic wave

the sequential ordering of stages along the length of the seminiferous tubule